Piezo-electric crystal



May 9, 1933.

Original Filed Dec. 19, 1928 FIG.

HG. J

g" U IIIIM i- .A MAR Isa/v ATTURNE Y Patented May 9, 1933 UNITED STATESPATENT OFFICE WARREN A. MARRISON', OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TOBELL TELEPHONE LABORATORIES, INCORPORATED, 013 NEW YORK, N. Y., ACORPORATION OF NEW YORK PIEZO-ELECTRIC CRYSTAL Original applicationfiled. December 19, 1928, Serial No. 327,017. Divided and thisapplication filed November 1, 1930.

This application is a division of my copending application Serial No.327,017, filed December 19, 1928.

This invention relates to piezo-electric crystals cut in the shape of aring or toroid, and means for mounting such crystals in an electricalcircuit.

The advantages of utilizing the piezo-electrio effect of substancespossessing such properties in the control of electrical oscillations ofconstant frequency have been known for some time. The uses for aconstant frequency control, and especially the need of control withinmore rigid limits, are constantly increasing. Such uses include thecontrol of broadcasting stations on their assigned wave lengths whetherlocally or upon transmission of a controlling wave from a. centralstation, and control of the frequency of the local oscillations in aheterodyne receiver. Frequency control means are also useful inconnection with sending and receiving sets in picture transmission andtelevision, in order to avoid the necessity of a synchronizationchannel, and similarly in systems of carrier wave telephony andtelegraphy, and are also important elements of laboratory referencestandards.

An object of this invention is to control the frequency of vibrations ofa piezo-eleetric crystal at a desired frequency.

A feature of this invention is the provision of electrodes for such aresonator which will permit control of its frequency vibra tion at adesired frequency by impressing a wave of such frequency on saidelectrodes. In my copending application, of which this application is adivision, it is disclosed that a ring-shaped piezo-electric quartzcrystal resonator the principal plane of which is parallel to theoptical and one of the electrical axes of the crystal may be cut to havea zero or approximately zero temperature coeificicnt of frequency, andthat certain advantages are inherent in the use of a resonator of thisshape in circumstances where it is desired to use a zero-coefficientcrystal.

If a ring of piezoelectric material. whether cut to have a Zerotemperature coefficient of frequency or not, is inserted bc- Serial No.492,669.

tween two electrodes whose length is equal to or greater than theoutside diameter of the ring, and whose width is equal to or less thanthe inside diameter of the ring, with the long side parallel to thedirection of the optic axis, it may be set into resonant vibrationhaving 4:, 6, 8 or any even number of nodes (within limits)approximately evenly spaced around the ring, by impressinga voltage onthe electrodes of the frequency of the resonant vibration desired. Ifthe electrodes cover one side only of the ring it may similarly be setin vibration.

In the drawing Fig. 1 is a diagrammatic plan of a toroidal resonatorwith electrodes covering part only of the plane surfaces of theresonator.

Fig. 2 is a diagrammatic plan of a toroidal resonator with electrodescovering the plane surfaces of one segmental portion only of theresonator.

Fig. 3 is an end View of Fig. 1 or Fig. 2.

In Fig. 1 a ring Q of piezo-electrically active quartz crystal, whichhas its principal plane parallel to the optical and one of theelectrical axes of the crystal is inserted between two electrodes Ewhose length is equal to or greater than the outside diameter of thering and Whose width is equal to or less than the inside diameter of thering. with the long side parallel to the direction of the optical axis.The ring may be set into resonance vibration having 4. 6, 8 or any evennumber of nodes (within limits) approximately evenly spaced around thering by impressing a voltage on the electrodes of the frequency of theresonance vibration desired. If the electrodes cover one side only ofthe ring as shown at E, Fig. 2, the ring may similarly be set invibration.

lVhat is claimed is:

1. A ring-shaped resonator and a pair of electrodes associated therewithadjacent oppositc faces of the ring and lying outside the space includedbetween the boundary planes of said opposite faces said electrodesoverlying a portion only of the adjacent faces of said ring.

2. A ring-shaped resonator cut from a. plate of quartz, the principalplane of which lie's parallel to the optical and electrical axes of thequartz, and an electrode associated with each plape faces of theresonator, each electrode having a length such that it extends entirelyacross both sides of its associated ring face and having a breadth suchthat it overlies less than half the surface area of said face.

3. A ring-shaped piezo-electric resonator of quartz, the principal planeof the ring, being parallel to the optical and electrical aXes of thequartz, and a pair of electrodes, each electrode disposed adjacent oneof the opposite faces of the ring to overlie a relatively small portionthereof whereby an electromotive force, which is an even multiple of thenatural resonant frequency of said element, applied to said electrodeswill set said ring in vibration at the frequency of said appliedelectromotive force.

4:. A toroidal shaped piezo-electric resonator of rectangularcross-section produced from slab of quartz, the principal plane of whichlies parallel to the optical and one of the electrical axes of thequartz crystal, a pair of similar plane electrodes of rectangular shapeassociated with the plane faces of said resonator, the length of whichis greater than the outside diameter of the toroid and is parallel tothe optical axis of the crystal, and the width of which is less than theinside diameter of the toroid, said electrodes being centrally locatedwith respect to the resonator whereby said resonator will vibrate at aneven harmonic of its fundamental frequency.

5. A quartz crystal piezoelectric resonator being in the form of atoroid of rectangular cross-section and a pair of electrodes associatedwith the opposite plane faces of a small sector of said resonatorwhereby said resonator will resonate at a harmonic of its fundamentalresonant frequency.

In Witness whereof, I hereunto subscribe my name this 31st. day ofOctober, 1930.

WVARREN A. MARRISON.

